104 ALASKAN GLACIER STUDIES
broad valley filled "with crevassed ice, and bordered by lofty, snow-clad mountain peaks, one of •which, Mount Hubbard, rises to an elevation of 16,400 feet at a distance of 8ft miles from the Hubbard Glacier front. In the absence of a more thorough survey we cannot be certain of the length of Hubbard Glacier, but from the evidence that we have the distance from its front to the head of some of its tributaries cannot be less than 80 miles and may be even as much as 50 miles. Doubtless it is made by the union of many tributaries of various sizes from Mount Hubbard, Mount Vancouver, and the mountains behind. It is probable that some of these upper portions of the Hubbard are through glaciers, feeding not only the Hubbard but also glaciers descending to the inland side of the mountain range, and possibly even directly connected with some of the feeders of Malaspina Glacier on the west, as they are known to be with Nunatak Glacier on the east.
The outer portion of Hubbard Glacier, with its ice cliff, is made by the union of two large arms, one from the direction of Mount Vancouver to the northwest, the other and larger from the Mount Hubbard region to the north. The northwest arm is a mile and a half or two miles wide, the north arm from two to three miles wide where it emerges from its mountain valley. Within the area visible from points on the fiord several relatively small tributaries, extend to each of these arms, descending the mountain valleys with steep grades and in some cases as cascading glaciers, or else with cascading ends just above their junction with the main glacier. Although small in comparison with the two main arms of Hubbard Glacier several of these tributaries are comparable in length and width with the ordinary valley glacier of the Alps. Each of the main arms of the glacier has a moderate grade within its mountain valley, the surface slope just inside the mountains being estimated to be about 5°; but. where they emerge from the mountains, and just above where they coalesce, the grade abruptly increases to twice that amount. As in the case of the Turner Glacier this steepened slope is interpreted as the result of the fact that the mountain valleys which the two arms occupy are hanging in relation to the main fiord valley. In the same way is the cascading condition of the lower ends of the tributaries to the two arms of the Hubbard interpreted as a result of the fact that these tributary valleys are hanging above the valleys in which the two main glacier arms lie.
Below the steepened slopes the north and northwest arms unite, forming a broad plateau with an undulating but nearly horizontal surface, broken by a labyrinth of crevasses and bristling with ice pinnacles, and faced by the ice nliff already described. "Whether any part of this terminus is afloat, or whether it all rests on the rock floor of its valley cannot be stated. At the base of the steepened slope the ice surface is only a few hundred feet above the fiord level, warranting the prediction that, if Hubbard Glacier should retreat, Disenchantment Bay would be extended several miles, and probably up to the base of the steepened slope.
Both the two arms and the low-lying ice plateau which their union makes are remarkably free from morainic d£bris (PL XLVI). This is in the main doubtless due to the fact that their rapid motion prevents the work of ablation from proceeding far enough to concentrate debris on the surface before reaching the front, where both ice and debris are floated away. A contributory cause for the absence of d6bris is the broadness of the valleys, by reason of which the avalanches in the lower valley portion cannot spread out toward the center of the glacier, while those that fall higher up are not revealed by